Watercress

The classic hazard of foraged watercress, and a documented human parasitic infection rather than a folk caution. Sheep and cattle grazing near water pass the eggs of the liver fluke Fasciola hepatica in their dung; the parasite develops through aquatic snails and then encysts on the surfaces of plants growing in that water. Watercress, which grows submerged in exactly the slow, snail-rich water below pasture, is the classic vehicle - human fascioliasis has been reported from wild watercress across Europe, South America, the Middle East and, less commonly, the United States. Infection causes fever, abdominal pain and liver damage that can appear weeks or months after the meal. The cysts are not visibly obvious and are not reliably removed by washing, salad spinners, vinegar or lemon juice. Heat destroys them. The same wild water can also carry E. coli, Giardia, agricultural nitrates and heavy metals from road runoff.

Watch for: Nothing on the plant itself - this is the point, and why the rule is about the WATER rather than the leaves. Assess the source instead: livestock, pasture, farmyards, manured fields or a septic field anywhere upstream; standing or slow-moving water rather than a clean cold spring; abundant small aquatic snails; road, ditch or storm-drain runoff entering above the patch. Any unknown or unassessable water source is by definition in this category.

Prevent: Grow your own in a container filled with mains or well water and you remove the risk entirely - this is the single reason home-grown watercress is a raw salad green with no caveats. For wild cress, look upstream before you pick: never gather below pasture, farmyards, manure, septic systems or road runoff. Rooting cuttings taken from a wild stand and growing them on in clean water gives you the same plant with none of the exposure, and is the standard forager's workaround.

Treat: COOK any wild-gathered watercress from water you cannot vouch for - a minute in boiling water, a stir-fry, or straight into soup destroys the cysts, and cooked watercress is excellent anyway. Do not rely on washing, soaking in vinegar or salt water, or a salad spinner. If you have eaten raw wild cress and later develop unexplained fever, right-sided abdominal pain or jaundice, tell a doctor specifically that you ate wild watercress: fascioliasis is treatable but easily missed without that history.

This is the whole reason watercress needs a safety note at all. Home-grown in clean water: eat it raw and enjoy it. Wild from unknown water: cook it. There is no third option worth taking.

Watercress grows in the same ditches, springs, streambanks and marshy ground as several members of the carrot family, some of which are among the most poisonous plants in North America. Water hemlock (Cicuta species) is the most dangerous: its cicutoxin causes violent seizures and death, sometimes within an hour, and the roots are the deadliest part. Poison hemlock (Conium maculatum) favors damp roadsides and ditch edges nearby. Lesser water-parsnip and fool's watercress grow tangled through cress stands in some regions and are commonly mistaken for it. The genuine risk is not usually confusing a whole plant but grabbing a handful of mixed greens from a wet patch and not looking closely at what came up in it.

Watch for: Any plant in the patch with FERNY, divided, carrot-like or parsley-like leaves rather than watercress's simple rounded leaflets along a hollow stem. Umbrella-shaped clusters of tiny white flowers - watercress has small four-petalled white flowers in a loose spike, not a flat umbel. Purple blotches or streaks on a stem, and a chambered rootstock that oozes yellow oily liquid when cut: those are water hemlock, and it is lethal. Any smell of parsnip, parsley or carrot when a leaf is crushed - watercress smells of mustard and pepper.

Prevent: Pick from a patch you can see clearly, in daylight, and look at each handful rather than raking through a stand. Learn the two shapes: watercress has a hollow, succulent stem with rounded leaflets in pairs along it and a terminal round leaflet, and it roots at the nodes; hemlocks have upright hollow stems with finely divided lacy foliage and flat-topped white flower umbels. Better still, sidestep the problem: take cuttings from a stand you have positively identified and grow them in a container at home, where you know exactly what is in the pot.

Treat: There is no treating a misidentification after the fact - if you are not certain, do not pick it, and if a gathered batch might contain anything else, discard the whole lot rather than sorting it. If someone has eaten a suspected hemlock, call poison control or emergency services IMMEDIATELY: water hemlock poisoning progresses to seizures very quickly and is a medical emergency, not a wait-and-see.

This risk belongs entirely to wild gathering. A container of watercress you sowed yourself contains only watercress, which is the strongest practical argument for growing it rather than foraging it.

Aphids are small soft-bodied sap-suckers - green, black, gray, pink, or waxy white, and mostly wingless - that gather in dense colonies on the tenderest new growth: shoot tips, buds, and the undersides of young leaves. They breed extremely fast in mild weather, so a few can become hundreds inside a week. Their feeding curls and distorts soft growth, and the sticky honeydew they excrete coats everything below and turns black with sooty mold. Ants often farm and defend the colonies for that honeydew. A few aphids are normal on almost any plant and a healthy plant shrugs them off; only dense, persistent colonies do real damage, and some aphids also spread plant viruses as they feed.

Watch for: Dense clusters of tiny insects packed onto shoot tips, flower buds, and the undersides of young leaves. Curled, cupped, or distorted new growth that never opens properly. A sticky shine on the leaves - and on whatever sits under the plant - that later goes black with sooty mold. Tiny white cast skins left behind where a colony has been feeding. Ants running steadily up and down the stems, which is often the first thing you notice. Mottled, streaked, or misshapen leaves that do not grow out can mean a virus the aphids brought with them rather than the feeding itself.

Prevent: Go easy on nitrogen: the soft, lush growth that heavy feeding produces is exactly what aphids breed on. Check new growth once a week through spring and early summer so you catch colonies while they are still small, and rub the first few out with your fingers. Leave flowering plants nearby and skip broad-spectrum sprays - ladybugs, lacewings, hoverflies, and parasitic wasps do most of this work for free, and they only stay if there is something for them to eat. Keep ants off the plant where you can, since they protect aphids from those predators. Water steadily so plants are not stressed, and check any new plant over before you bring it home or move it indoors, since aphids usually arrive on something else.

Treat: Knock the colonies off with a hard jet of water and repeat every few days - on most plants that alone ends it. Pinch out or prune off the worst-infested tips rather than treating the whole plant. If colonies keep rebuilding, spray insecticidal soap or horticultural oil directly onto the insects, covering leaf undersides, and repeat weekly until they are gone; treat early or late in the day, and never spray a wilted or heat-stressed plant. Avoid broad-spectrum insecticides - they kill the ladybugs, lacewings, and parasitic wasps that were about to solve the problem for you, and aphid numbers usually come back worse afterward. Anything you spray must be labeled for the plant you are treating; follow that label and observe its pre-harvest interval. On anything you eat, wash leaves, heads, and buds well before use, since aphids hide down in crowns, folds, and tight growth.

Watercress is picked whole and eaten raw, so aphids sheltering deep in the crowded stem bases are as much a washing problem as a plant-health one - rinse cut sprigs thoroughly. A hard rinse of the whole stand with clean water usually clears a colony, and cutting the crop back hard removes the rest.

Slugs and snails are nocturnal mollusks that rasp ragged holes in soft leaves, shear off seedlings at ground level, and chew into ripe fruit that touches the soil. They feed at night and in the early morning and spend the day hidden under boards, pots, dense mulch, leaf litter, and low foliage, becoming active in exactly the cool, damp, shaded conditions that suit young plants. Damage is heaviest in wet spells and on tender spring growth: a single wet week can erase a row of seedlings while an established, tough-leaved plant of the same species is barely marked. They lay clusters of small pearly eggs in damp soil and under debris, so a garden with plenty of cover carries a resident population year after year rather than being invaded from outside.

Watch for: Irregular ragged holes chewed out of the middle of leaves and along the edges - not the clean-edged cuts a caterpillar leaves. Seedlings that vanish overnight, or that are cut off at soil level with nothing left behind. Silvery dried slime trails across leaves, soil, pots, and paving in the morning: this is the giveaway that tells you it was mollusks rather than an insect. Chewed pits in ripe fruit, especially where it rests on the ground. Damage that shows up on the lowest, dampest leaves first and gets worse after rain or evening watering. Turn over a board, an upturned pot, or a clump of dense mulch during the day and look for the animals themselves sheltering in the cool underneath.

Prevent: Take away the daytime shelter first: lift boards and upturned pots, clear piles of debris, keep dense mulch pulled back from crowns and stems, and give crowded plantings enough airflow to dry out. Water in the morning rather than the evening so the surface is dry by the time they come out. Copper tape around containers and raised beds gives them a shock they will not cross, and it is the one barrier that reliably works. Get plants past the vulnerable stage quickly - start seedlings in pots and set them out at a decent size rather than direct-sowing into a cold wet bed, since most plants stop being worth defending once the leaves toughen. Leave the ground beetles, frogs, toads, and ground-feeding birds alone, because they eat mollusks all night for free and broad-spectrum slug pellets kill them too. Where thick-leaved or resistant varieties exist for what you are growing, they take far less damage.

Treat: Hand-picking works and costs nothing: go out an hour after dark with a headlamp, drop what you find into soapy water, and repeat nightly for a week or two - persistence is what wins, not any single product. Shallow beer traps sunk to soil level catch them too, but need emptying and refilling daily to be worth anything. Iron-phosphate bait is the standard control and is far lower-risk around pets and wildlife than the old metaldehyde products, but it is not harmless: many formulations include EDTA, and a dog that eats a quantity of pellets can develop iron toxicosis. Scatter it thinly per the label, never in piles, and keep dogs off a baited bed. Clear fallen foliage and debris in autumn, where the eggs are laid. In a wet climate this is a population you manage each season rather than one you eradicate - and on most established plants light grazing is cosmetic and needs nothing at all.

A permanently wet container is ideal slug and snail habitat, and small aquatic snails also colonize standing water. Copper tape around the rim of the tub is unusually effective here, and rinsing cut sprigs matters because small snails hide in the crowded stem bases.

Flea beetles are tiny dark beetles - often shiny black or bronze, rarely more than a couple of millimeters long - with enlarged back legs that let them spring away like fleas the moment you lean in. The adults chew countless small round pits and shot-holes through leaves, giving the foliage a peppered, buckshot-riddled look. They overwinter as adults in leaf litter, hedgerows, and crop debris, emerge hungry in spring, and are worst in warm dry spells. The damage is mostly a seedling and transplant problem: a small plant with a few leaves can be checked, stunted, or killed outright, while the same plant shrugs them off once it is large and growing strongly. Different species specialize on different plant families, so the beetles hammering your brassicas are not the ones on your nightshades. Some species also have larvae that feed on roots and tubers underground.

Watch for: Dozens of pinhead-sized round holes peppered across the leaves, thickest on the youngest, most tender growth. Tiny beetles that spring away as you brush the plants or lean in for a closer look - that jump is the identification. Seedlings that go lacy and stop growing, and transplants that sit and sulk instead of taking off. Damage heaviest in warm, dry weather and along the edge of a bed nearest weedy ground or last year's crop debris. On root crops, shallow narrow grooves or channels scarring the skin at harvest, from larvae feeding underground.

Prevent: Floating row cover or fine insect mesh, laid over the bed from the day of sowing or transplanting and sealed at the edges so nothing can walk in underneath, is the single best defense - and on the crops they favor it is close to essential. Leave it on until plants are large and growing strongly, or until flowering on anything that needs pollinating. Push growth: a well-watered, unchecked plant outgrows the damage, so the whole game is getting seedlings through their vulnerable weeks fast. Keep beds weed-free, since related weeds host the beetles alongside your crop, and clear crop debris at the end of the season where the adults overwinter. Rotate away from a bed that grew a related crop last year. Where you can, shift sowing dates - cooler-season and fall plantings often miss the peak of adult feeding entirely.

Treat: Row cover and healthy fast growth carry most crops through, and on an established plant the damage is usually cosmetic and needs nothing at all. Where a young planting is genuinely being stripped, kaolin clay coats the leaves and deters feeding, and spinosad will knock the beetles back. Spinosad is acutely toxic to bees while the spray is still wet - apply it at dusk when bees are not flying, never onto plants in flower, and follow the product label. Anything you spray must be labeled for the plant you are treating, and you must observe its pre-harvest interval on a crop you are picking. Yellow sticky traps are useful for telling you when the beetles have arrived. Where the damage falls on the part you eat, harvesting young often beats them outright; where you are growing for a root or a fruit, leaf damage can simply be tolerated. Larvae feeding underground cannot be reached by a foliar spray, so rotation and clean beds are what work against those.

The leaf is the crop here, so shot-holes are a real loss rather than a cosmetic one. A fine mesh cover over the container from sowing is the practical answer, and it also keeps cabbage whites off; damage is worst on a container sitting in a warm dry spot, which is the wrong place for watercress anyway.

The characteristic disease of watercress grown in standing or recirculating water, caused by the soil-borne organism Spongospora subterranea f. sp. nasturtii, which also carries a virus that worsens the symptoms. It infects the roots, which swell, twist and turn crooked and brown instead of running white and straight, so the plant cannot take up water and nutrients properly. Growth stalls, leaves yellow and redden, and stands thin out. It is favored by cool water, which is why it is mainly a winter and early-spring problem, and it persists in contaminated water, containers and old plant material.

Watch for: Roots that are short, swollen, brown and bent rather than white and straight - lift a plant and look. Stunted growth and small leaves with yellow or reddish-purple tints, particularly in cool weather. A stand that stops regrowing after cutting. Symptoms spreading through a container from one area outward.

Prevent: Use clean water from a mains or well source rather than pond, ditch or stream water, and do not reuse water from an affected container. Start with clean seed or cuttings from a healthy plant, not material from a wild stand or an ailing pot. Wash out containers and trays between crops. Keep water moving and refreshed rather than stagnant, and avoid crowding.

Treat: There is no home cure for an infected stand. Discard the affected plants and the water, scrub and dry the container, and start again from seed or from cuttings taken off a clean plant. Since the organism travels in water and debris, sanitation between crops is the whole control.

Rare in a small container run on fresh mains water and changed regularly, which is another reason to keep tipping and refilling. Most cases in home culture trace back to using pond or stream water.